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UNITED sTATEs PATENT oEEIoE.

A. H. BLACK AND C. R. BLACK, OF INDIANAPOLIS, INDIANA.

HYGROMETER.

Specification of Letters Patent No. 31,773, dated March 26, 1861.

To all whom tt may concern:

`Be it known that we, A. H. BLACK and C. R. BLACK, both of Indianapolis, in the county of Marion and State of Indiana, have invented a new and Improved Hygrometer, which we term The Natural 11V eat-her- Guideg and we do hereby declare that the following is a full, clear, and exact description of the same, reference being had to the accompanying drawings, forming part of this specication, in which- Figure l is a face view of the instrument. Fig. 2 is a central vertical section of the same. Fig. 3 is a side view representing the operating portion of the instrument detached. Fig. 4c represents the seed and twisted awn of a grass of the order stipa such awn constituting the principal element of our instrument.

Similar letters of reference indicate corresponding parts in the several figures.

To enable others to make and use our invention we will proceed to describe its con struction and operation.

A is a board or case upon or within which is the dial a, from the center of which there lis a hole through the back of the board or box for the reception of a plug b, of wood 0r` other material in the center of which is inserted and secured one end of the twisted axis c, composed of a portion of the length of the awn represented in Fig. 4. The twisted axis has secured to it at or near its opposite end, which 4projects through. an opening in the center of the dial, the index CZ.

e, is a glass, covering the index and dial but having a hole in the center for the admission of the atmosphere around the axis o.

f, is a pointer, fitted to the hole in the center of the glass e, in such manner as not to obstruct the entrance of air through the said hole, and in such manner as to be capable of adjustment by hand outside the glass for the purpose of showing what may have been the position of the index d, at a certain time.

As the twisted axis c, t-wists and untwists itself with the changes in the hygrometric condition of the atmosphere, the index is caused to turn in one direction or the other, and, by a proper' system of graduation of the dial, may be made to indicate the degree of moisture in the atmosphere. If the twisted axis c, be ofconsiderable length it will make more than a complete revolution between the extremes of `the hygrometric condition otl the atmosphere, and in fact it nearly the whole awn be used for the axis'it may make even three or four revolutions, and as these could not be traced upon the dial without very constant watching, we propose to use in some cases the supplementary index g, which is made in the form of the letter L, as shown in Figs. 2 and 3, and secured to the twisted axis at a suitable point between where it is secured in the plug I), and where the index el, is attached, and when this index A. H. BLACK. C. R. BLACK. Witnesses: Y

ALEXANDER H. CAMER, J. H. SEYBOLD. 

